1. Field of the Invention
The present invention relates generally to a plate-like electric conductor for a busbar and a busbar formed therefrom, and more particularly to a plate-like electric conductor for a busbar, which has high degrees of electric conductivity, strength and bendability, and a busbar consisting of the electric conductor having such properties.
2. Discussion of Related Art
Plates made of a pure copper material having a high degree of electric conductivity such as oxygen-free copper, tough pitch copper and phosphorus-deoxidized copper are conventionally used for an electric conductor for a busbar employed for a power control unit (PCU) for bullet train (Shinkansen) cars, linear motor cars and hybrid motor cars. Plates made of a copper alloy material having a high degree of electric conductivity and subjected to Ni electroplating are used when the electric conductor is required to have a higher degree of strength. However, costs of the copper and copper alloy materials are rising along with a recent increase of resource costs. Also, the copper and copper alloy materials have relatively heavy weights and are not preferred for components of vehicles, which are required to have reduced weights to improve fuel economy of the vehicles. Therefore, an alternative material having a lighter weight and a lower cost is desired for the electric conductor. Further, the Ni electroplating has a potential problem of a high cost.
In view of the above-described problems, aluminum (Al) has been attracting attention as an alternative material for the electric conductor for the busbar, owing to its low cost and contribution to reduction of weight. Among aluminum materials having an industrial pure level, A1060 aluminum material according to JIS is advantageously used since this material is considered to be particularly effective to achieve an electric conductivity of 61% IACS, as disclosed in JP-A-2011-19385, for example. Further, a 6,000 series aluminum alloy material such as A6061 aluminum alloy material according to JIS or ISO is used when the electric conductor is required to have a higher degree of strength, as disclosed in JP-A-2011-19385 and JP-A-2009-238831, for example.
There is a recent demand for a busbar which can be formed into a complex shape so as to be adapted to a surrounding environment in which the busbar is to be installed. Therefore, the busbar is required to have a high degree of bendability as well as high degrees of electric conductivity and strength. However, the conventional electric conductors for the busbar made of a pure aluminum material or an aluminum alloy material have problems that the electric conductor satisfying some required degrees of electric conductivity and bendability cannot have a sufficiently high degree of strength, while the electric conductor satisfying some required degrees of electric conductivity and strength cannot have a sufficiently high degree of bendability. Thus, the conventional electric conductors cannot satisfy required degrees of all of the electric conductivity, strength and bendability. This results from mutually contradictory requirements for achieving these properties, namely, it is preferable to precipitate solute components in the aluminum or aluminum alloy as much as possible in order to achieve the sufficiently high degrees of electric conductivity and bendability, while at the same time it is preferable to prevent the precipitation of the solute components as far as possible in order to achieve the sufficiently high degree of strength owing to a solute effect.